Fuzzy logic control (FLC) has been widely applied to the industrial environment in recent years. Although many of the applications are relatively small in scale, such as in washing machines, elevators, automobiles and video cameras, there is a considerable amount of interest in applying fuzzy logic systems to process control. In the field of process control, research has been conducted into the use of FLCs similar to conventional Proportional, Integral, Derivative (PID) controllers.
In typical applications, an operator will set up a FLC by adjusting certain control parameters that exist within the controller, in order to attempt to optimize the response performance of the controller. While manual tuning of fuzzy logic controllers is possible, it is often tedious and error prone. Moreover, the process under control may change over time, thus requiring retuning.
Automatic tuning approaches have been applied to process controllers and their variants. For example, in U.S. Pat. No. 4,549,123, and in application Ser. No. 08/070,090, now U.S. Pat. No. 5,453,925, filed May 28, 1993 (assigned to the same assignee as the present application), the disclosures of each of which are incorporated herein by reference, a controlled induced oscillation procedure is used in order to determine the ultimate gain, ultimate period and time delay of the process under control. Once these process characteristics are derived, tuning rules are used to determine the process control parameters of the PID controller.
However, to date, there have been no methods or means proposed for the automatic tuning of fuzzy logic controllers, thus leaving an operator with only trial and error manual tuning.